Extra Front Desk Line for two offices and one front desk phone with two businesses!

We have two offices that run two dba's out of them. We currently have live answering rather than auto answer. We now want to add the second dba to our current phone system with a separate number but want to know how we do that and how we will be able to know which entity this is coming into so that we answer the line with the correct entity name. Help????

So we wouldn't need a separate business line? Just an extension? Would I see that extension on my user end to be able to identify how I answer that business entity call? So no separate business line would be required?